1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member sensitive to electromagnetic waves such as light (which is light in the broad sense of the word and means ultraviolet rays, visible rays, infrared rays, X-rays, γ-rays, etc.).
2. Related Background Art
A photoconductive material which forms a photoconductive layer of an electrophotographic photosensitive member is required to have high sensitivity, a high SN ratio [photocurrent (Ip)/dark current (Id)] and an absorption spectrum suited to the spectral characteristics of the light with which the photoconductive material is irradiated, and to be harmless to the human body during use, and amorphous silicon (referred to also as “a-Si”) which exhibits excellent properties in this respect and in particular, hydrogenated amorphous silicon (referred to also as “a-Si:H”) has hitherto been put to wide application.
In general, a conductive substrate is heated to 50° C. to 350° C. and such an a-Si-based photoconductive material is formed on this substrate by film deposition methods such as the vacuum evaporation method, the sputtering method, the ion plating method, the thermal CVD method, the optical CVD method and the plasma CVD method. Among others, the plasma CVD method, i.e., a method by which a raw material gas is decomposed by high frequency or microwave glow discharge and an a-Si:H deposited film is formed on a substrate has been widely used as a favorable method.
In recent years, in association with the widespread use of computers in offices and general homes and the digitization of sentences and images, electrophotographic apparatus as output units have also been digitized and the formation of latent images by use of a light source the main component of which is single wavelength has becoming mainstream. On the other hand, as a result of improvements of an optical exposure device, a development device, a transfer device, etc. within an electrophotographic apparatus, also in electrophotographic photosensitive members, an improvement in the image characteristics has also begun to be required more than before.
In a conventional electrophotographic photosensitive member, in order to make improvements in the electrical, optical and photoconductive characteristics, such as dark resistance value, photosensitivity and optical response, the environmental characteristics such as moisture resistance the and temporal stability of a photoconductive member having a photoconductive layer formed from a-Si deposited film, electrical potential characteristics excellent in electric charging capacity and optical sensitivity are obtained by providing a surface barrier-wall layer formed from a non-photoconductive amorphous material containing silicon atoms and carbon atoms on a photoconductive layer formed from an amorphous material constituted by silicon atoms as a base material, as described, for example, in the Japanese Patent Application Laid-Open No. S57-115556.
Furthermore, in some conventional electrophotographic photosensitive members, as described in the Japanese Patent Application Laid-Open No. H06-242623 (U.S. Pat. No. 5,556,729), excellent electrophotographic characteristics are obtained by providing, between a photoconductive layer and a surface layer of an electrophotographic photosensitive member for negative charging, a hole capturing layer which is mainly formed from amorphous silicon and either contains less than 50 ppm of boron by atom or does not contain any element governing conductivity.
Also, in some cases, as described in the Japanese Patent Application Laid-Open No. H11-242349 (U.S. Pat. No. 6,238,832), an electrophotographic photosensitive member of high image quality excellent in electrical characteristics which does not develop exfoliation, damage and wear after use for a long time is obtained by causing at least oxygen, nitrogen, fluorine and boron atoms are all to be simultaneously contained in a surface layer of the electrophotographic photosensitive member.
Although good electrophotographic photosensitive members have been realized owing to the technological development as described above, the level of market requirements for products which are produced is becoming higher day by day and higher-quality electrophotographic photosensitive members are demanded.
Particularly, in digital electrophotographic apparatus and digital full-color electrophotographic apparatus which have come into remarkable widespread use, copies of not only originals in letters, but also photographs, pictures, design drawings, etc. are frequently generated and, therefore, an improvement in dot reproducibility has become required more than before. For example, when high resolution is to be achieved by decreasing the dot pitch of an image, dot reproducibility may sometimes become unstable, thereby causing the image flow phenomenon. Also, simultaneously, as a challenge to higher image quality, it has become more required than before to reduce optical memories represented by the ghost phenomenon and to increase sensitivity.
In order to solve these problems, the optimization of layer construction and film quality improvements for digital exposure and the control of element contents have been carried out as described above. However, as described above, the level of market requirements for images is very high and further improvements in image characteristics are strongly demanded. In recent years, electrophotographic photosensitive members used in digital electrophotographic apparatus have been required to provide higher durability than before. When the film thickness of a surface layer is increased in order to meet this requirement, a charge carrier which forms a latent image becomes apt to diffuse laterally. For this reason, dot reproducibility may sometimes become unstable and a technique for controlling the lateral diffusion of a charge carrier is strongly demanded.
In digital full-color electrophotographic apparatus, a negative toner which has the widest range of material selection as a color toner as the most common combination of charging, development, etc., and an image exposure method (a method of exposing image portion) which provides high controllability of latent images and is suitable for high image quality design are conceivable, and on that occasion, it is necessary to cause a photosensitive member to be electrically charged with a negative electric charge. In an a-Si-based photosensitive member for negative electrification which has hitherto been devised in digital full-color electrophotographic apparatus, it is desirable to provide an upper charge injection blocking layer in order to block the injection of negative charges from the surface as much as possible, and how to improve a non-single-crystal layer region constituted by silicon atoms and carbon atoms as base materials, including this upper charge injection blocking layer, is a clew to improvements in the characteristics.
Particularly, with respect to the recent requirements for digital full-color electrophotographic apparatus, overall improvements in the characteristics of photosensitive members to a greater extent than before have become necessary. And there is a case where the distance from a charging device to a developing device becomes apt to increase because for example, as one of the process conditions, a plurality of developing devices are provided around an electrophotographic photosensitive member or large-sized developing means are used. For this reason, in order to compensate for a decrease in potential from a charging device to a developing device due to dark attenuation, it is necessary to raise the charge potential more than before and hence an upper charge injection blocking layer is becoming more and more important.